AS & A Level Biology - 9700 Paper 2 2021 Winter Zone 3

(a) (i) Name the stage of protein synthesis that is shown in Fig. 1.1.
.................................................................................................................................................... [1]
(ii) Identify A, B and C in Fig. 1.1.
A ......................................................................................................................................................
B ......................................................................................................................................................
C ...................................................................................................................................................... [3]
(iii) State the base sequences at D and E.
D ...................................................................................................................................................
E ................................................................................................................................................... [1]

(b) Mutagenesis is a process that leads to a change in the amino acid sequences of proteins. Scientists carry out mutagenesis to investigate the importance of particular amino acids in protein structure and function.
Outline how changing one amino acid in the β-globin polypeptide of haemoglobin may change the structure and function of a molecule of haemoglobin.
.................................................................................................................................................................. .................................................................................................................................................................. .................................................................................................................................................................. .................................................................................................................................................................. ................................................................................................................................................................. [4]

Pepsin is an enzyme that hydrolyses proteins (protease). Some students used pepsin from the stomach of a mammal.

The activity of the pepsin was investigated by placing a small quantity of the enzyme with a known concentration of the protein albumen.

Fig. 2.1 shows the progress of the enzyme-catalysed reaction that was carried out at 20 °C.



(a) Calculate the initial rate of the reaction.

initial rate of reaction = ..................................................... [2]

(b) (i) The procedure was repeated to find the effects on the activity of the pepsin using a competitive inhibitor at the same temperature, 20 °C.

Predict the results that will be obtained using the competitive inhibitor.

...............................................................................................................................
...............................................................................................................................
...............................................................................................................................
............................................................................................................................... [2]

(ii) The procedure was repeated without the competitive inhibitor but at the higher temperature of 30 °C.

Predict the results that will be obtained at 30 °C.

...............................................................................................................................
...............................................................................................................................
...............................................................................................................................
............................................................................................................................... [2]

(c) The students extended their investigation by using pepsin from a different species of mammal. The experiments were carried out at 20 °C and without a competitive inhibitor.

With reference to Fig. 2.1, explain the advantage of calculating the initial rate of reaction in each experiment.

...............................................................................................................................
...............................................................................................................................
...............................................................................................................................
...............................................................................................................................
............................................................................................................................... [2]

(a) (i) Explain how the cells in the capillary shown in Fig. 3.1 can be identified as red blood cells. ...............................................................................................................................................
........................................................................................................................................................
........................................................................................................................................................
........................................................................................................................................................
........................................................................................................................................................ [3]

(ii) Capillaries are surrounded by tissue fluid.
Outline the ways in which the composition of tissue fluid differs from blood.
........................................................................................................................................................
........................................................................................................................................................
........................................................................................................................................................ [2]

(b) Scientists compared features of the physiology of three groups of people who live at different altitudes. These people were selected from populations that have lived at these altitudes for many thousands of years.

The scientists took blood samples from people in each location and measured:
• the concentration of haemoglobin in the blood
• the percentage saturation of haemoglobin with oxygen in blood leaving the lungs
• the oxygen concentration in the blood leaving the lungs.

The results are shown in Table 3.1.

[Table_1]

(i) Describe the changes in mean percentage saturation of haemoglobin with oxygen and the mean haemoglobin concentration in blood as altitude increases.
........................................................................................................................................................
........................................................................................................................................................
........................................................................................................................................................
........................................................................................................................................................
........................................................................................................................................................
........................................................................................................................................................ [3]

(ii) With reference to Table 3.1, suggest how the people living at high altitude can have an oxygen concentration in blood leaving the lungs similar to that of the people living at sea level.
........................................................................................................................................................
........................................................................................................................................................
........................................................................................................................................................
........................................................................................................................................................
........................................................................................................................................................
........................................................................................................................................................ [3]

In thale cress, Arabidopsis thaliana, most of the stomata are on the lower surface of the leaves.

Fig. 4.1 is a diagram of an open stoma and two guard cells. Some of the cellulose fibres in the cell wall of the guard cells are shown.



(a) The cellulose fibres shown in Fig. 4.1 are composed of bundles of cellulose microfibrils. Explain how molecules of cellulose are arranged into a microfibril.
........................................................................................................................................................
........................................................................................................................................................
........................................................................................................................................................
........................................................................................................................................................
........................................................................................................................................................ [2]

(b) The width of stomatal openings in A. thaliana is regulated by movement of ions. These ions move through channel proteins in the cell surface membranes of the guard cells.

(i) Draw a diagram to show part of a cell surface membrane with a channel protein. Label your diagram.

[3]

(ii) Explain why channel proteins are needed for the movement of ions into and out of cells.
........................................................................................................................................................
........................................................................................................................................................
........................................................................................................................................................
........................................................................................................................................................
........................................................................................................................................................ [2]

(c) The outward movement of ions from guard cells causes stomata to close. A variety of A. thaliana does not have channel proteins for the outward movement of ions in the cell surface membranes of the guard cells. Suggest and explain the effect of not having these channel proteins on transpiration.
........................................................................................................................................................
........................................................................................................................................................
........................................................................................................................................................
........................................................................................................................................................
........................................................................................................................................................
........................................................................................................................................................
........................................................................................................................................................
[3]

Measles is a highly infectious disease. The World Health Organization (WHO) has coordinated a programme for controlling this disease by using vaccination.
(a) (i) Name the pathogen that causes measles.
......................................................................................................................... [1]
(ii) Explain how the measles pathogen is transmitted.
...................................................................................................................
...................................................................................................................
...................................................................................................................
...................................................................................................................
................................................................................................................... [3]
(b) Fig. 5.1 shows the number of cases of measles globally each month between January 2015 and March 2019.
!(Graph depicting the number of measles cases globally)
Describe the pattern of measles cases as shown in Fig. 5.1.
...................................................................................................................
...................................................................................................................
...................................................................................................................
...................................................................................................................
................................................................................................................... [3]
(c) Explain why measles has not yet been eradicated even though a vaccine has been available since the 1960s.
...................................................................................................................
...................................................................................................................
...................................................................................................................
...................................................................................................................
...................................................................................................................
...................................................................................................................
...................................................................................................................
................................................................................................................... [4]
[Total: 11]

(a) Table 6.1 compares some of the features of DNA with the protein collagen.
Complete Table 6.1.

Table 6.1

| feature | DNA | collagen |
|----------------------------------|----------|----------|
| elements | | C H O N |
| monomers | | |
| bond between monomers | | |
| site of production in eukaryotic cells | nucleus | |

[6]

(b) Most of the DNA in a eukaryotic cell is located in the nucleus.

State how the structure of a nucleus is suited to its function of containing DNA.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................

[2]

(c) Fibroblast cells produce elastic fibres and collagen fibres in lung tissue.

Describe the function of elastic fibres in lung tissue.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................

[2]

(d) Name the stage of the cell cycle during which DNA and proteins are synthesised.
..........................................................................................................................

[1]